Picture transmission



1932. A. v. BEDFORD 1,849,818

PICTURE TRANSMISS ION Filed Sept. 19, 1930 2 Sheets-Sheet l lnvefitorz Aida V. Bedfor'd,

l-lLs Attorney "March 15, 1932. A. v. BEDFORD PICTURE TRANSMISSION Filed Sept: 19, 1930 2 Shee tS-Shet 2 Inventor. Aida \/.Bedf-'br-d. y

' HLs'Attor-ne g.

4 Fig.5.

Patented Mar. 15, 1 932 snares Pram i oFFIca TRIG COMPANY, A COBBORATION OF NEW YORK morons 'riaansrrrssron Application filed September 19, 1930. Serial No. 483,033.

My invention relates to the transmission of pictures and particularly to the transmis sion of moving pictures or to television.

One of the dificulties encountered in pres- 5 ent television systems is that of obtaining faithful amplification of the transmitted impulses, over the wide range in frequency of such impulses heretofore found necessary. For example it is commonly considered that the lowest frequency which the amplifier should be able to handle with fidelity is that which corresponds to the transmission of a picture or view in which the upper half is light and the lower half is dark (or vice versa), the scanning being horizontal. For a 60 line picture transmitted at the rate of pictures per second thiswould require a minimum frequency of 20 cycles per second. The

highest frequency, considering the obtaining 20 of equal definition up and down and from right to left of the picture, would be 36,0 00 cycles per second. It is the object of my 1nvention to provide an improved television system wherein the necessary frequencyrange is greatly reduced, thereby partially if not entirely removing the aforementioned amplification difficulty.

As a result of my invention the minimum frequency which must be amplified, such as with a picture which is half light and half dark as described above is raised from the number of pictures per second to the number of scanned lines per second. Thus in the case of the example given above the minimum frequency which the amplifier must handle is raised from 20 to 1200 cycles per second.

Inaccordance with myinvention I scan the object whose image is to be transmitted and produce impulses corresponding to the 40 shade variations in each line in the usual and well known manner. Invariably the light areas and dark areas scanned in a single line will not total the same but the one or the other will predominate, the positive and negative values of the impulses due to the light and dark areas likewise predominating the one over the other.

such a sign andof such value that when added to the impulses of that line a complete balance'is effected. ,This in effect correctly 10- cates the zero of the alternating picture frequency wave.

My invention will be better understood At the end of each line scanned I-produce an auxiliary impulse of 2 shows a modified form of same; and Fig.

3, 4 and 5 are diagrams illustrating the theory of my invention.

Before describing the apparatus shown in Figs. 1 and 2, I shall first briefly describe the theory of my invention with the help of Figs. 3, 4 and 5. In each of these figures the distance A represents the time during which one line of the picture to .be transmitted is scanned, and B represents the time devoted to the auxiliary signal impulse. In Fig. 3 it is assumed that the entire scanning line lies in a dark portion of the picture and that the resulting impulse is positive for the dark portion of the picture. The positive rectangular loop 1 therefore represents this scanning line of the picture. At the end of the line a negative impulse is produced which is proportional to the aforesaid positive impulse. This negative impulse is represented by the negative loop 2 whose area is proportional to the area of loop 1. A complete cycle is therefore produced for this scanning line and the zero line 0 is correctly located. In Fig. 4 it is assumed that the scanning line is uniformly dark for the first half of the line and uniformly light for'the second half of the line. 3 and the negative loop 4 are equalto' eachother and. no auxiliary signal impulse is Consequently, the positive loop i line represents the impulses when the scanneeded to producea balance. In Fig. 5 the mug line contains varying amounts of light and dark areas. 'At the 'endof the hnean ,auxiliar signal loop. 6 is shown of positivevalue w ich is equal to the sum of the two negative loops 7 and 8 minus the positive loop 9. The total positive and negative areas of the main signal impulse and the auxiliary signal imnpuls'e therefore are equal;

I she now describe the apparatus by which this result is eflected. In Fig. 1, I have shown the scannin device of a well known form comprising't e disc lOhaving a spiral roll of holes 11 therein connected to be driven by the'motor 12- and the photoelectric cell 13 for receiving light reflected from the object being scanned. At 15 I have shown a contactor-device comprising the rotatable arm 16- adapted successively to sweep over the long segment 17 and the two short segments 18 and 19. Arm 16 is rotated in synchronism with the scanning disc 10 being arranged to make one complete rotation for each scanning line. For this purpose I have shown the arm 16 connected by the shaft 20 with the shaft of the disc 10 through the gearing 21. It will be understood that the scan- 'ning mechanism illustrated is merely representative of any suitable scanning mechanism which may be connected in any desired manner with the contactor device 15.

' The signal impulses produced by the photoelectric'cell 13 are amplified by the electron discharge amplifier 23 whose output circuit connects through a portion of battery 24 with the long segment 17 of the contactor 15.

Contact arm 16 connects throu h condenser 25 with the grid of electron disc arge amplifier 26 whose plate-circuit leads through condenser 27 tothe output circuit 28. The impulses in this circuit may be transmitted to adistant receiving station by radio, wire line or any other suitable'means. The signals received from,the photoelectric cell are in part further amplified by the thermionic amplifier 30 whose grid connects with the battery 24'and whose plate connects with battery 31-through the variable resistance 32. The adjustable contact 33 of this resistance connects through resistance 34 with the'condenser 35 whereby the condenser-is charged to a level dependent upon the drop in potential. across that part of resistance 32 between the adjustable Contact 33 and battery 31. Condenser 35 is shown shunted by the resistance 36 which controls the time constant of the condenser. Battery 37 is connected between contactor segment 18 and that side of the condenser 35 which connects with the resist ance 34. Segment 19 of the contactor connects directly with the opposite side of the condenser.

In the operation of the apparatus "above described the object whose image'is to be transmitted is scanned in the usual and well known manner, the signal impulses from the photoelectric cell after amplification by the amplifier 23'being transmitted through the. long segment 17-.and arm 16 of the contactor device l5fto the amplifier 26 and thence to the output circuit 28. The long segment. 17 of the contactor deviceis of such-a length that the arm 16- remains in contact there with during each scanning line and signal inipulses. are transmitted during that time in the usual manner. During the scanning of v the line the varging current flow in the plate circuit of ampli er 30 due to the varying lightand dark portionsof the line produce a corresponding charge in the condenser 35. At

the end of the line the arm 16 passes from the segment 17 to segment 18 .without short,

circuiting-17 and 18. While the arm engages segment '18 the output circuit is in connection with the condenser 35v and battery 37.

of the battery, it will act through the battery sending an lmpulse of one sign to-the outputficircuit and if the battery has a greater voltage than the condenser the battery will an energy storing means, the energy flowing In this a If the voltage of the condenser exceeds that into the condenser from battery 31 during the scanning of a line being considered as a posi tive storage and the energy flowing out of 7,-

the condenser during such scanning being considered a negative storage; At the end-of each scanning line the resulting voltage of condenser 35 is compared to that of battery. 37 If the two voltages happen to be equal, 3.

no auxiliary impulse is produced. If the condenser voltage is less than that of battery 37, animpulse of one sign is produced and if the voltage of condenser is greater than that of the battery, an auxiliary impulse of the .1;

opposite sign is produced. In each case the magnitude of the impulse is proportional to the difference between the light and darl? portions of the scanning line. Thus the auxiliary signal is such as to cause the amplifier system essentially to recover its equilibrium after its unbalanced condition resulting from any lack of equality of dark and light signals from each line.- In the distant receiver illumination of the recording light during the time of the auxiliary signal is not desired since it forms no part of the picture-and therefore should preferably be masked oflby a suitable screen or barrier placed along either the right 'or ture. This light as far asthe received picture is concerned is superfluous and existssolely because of the apparatus for keeping the picture in balance. The above described system I have accordin ly called the scrap pile border system. ince a lamp in the plate circuit of anyA. C. ampl fier tends to supply a constant value of average light, whenever anyline of the picture has other than this avdrage amount of light, the difference either positive or negative issupplied by the scrap pile.

In Fig. 2 I have shown a modified form of my invention in which the amplifiers 23 and are coupled not for the amplification of direct current but for a low frequency alternating current since it is desired that they handle the picture fregpency; In this form of my invention the C. component of the potential applied to segment 18 is adapted, to be manually controlled by the use of the adjustable resistance 40, I may, however, employ an auxiliary photoelectric cell to control this potential in accordance, with the general illumination of the picture.

While I have shown the contactor 15 as comprising the three segments, I may employ a 'contactor having a greater number of contacts. For example, the number of contacts may be multiplied by ten whereby the speed at which the arm must rotate would be reduced to one tenth 0t that necessary when but three contactors are employed.

From the above description it will be seen that in accordance with my invention the average illumination of a picture 15 con- I trolled by the illumination of the object whose image is being transmitted. This advantage becomes particularly important in the case of multiple light source colored television, since without ability to control the average intensity of each color in the received picture, every picture would have the same average amount of each color in it re gardless of how much of each of those colors there was in the original object. For example, if no red were present in the object, red light would not be forced into the receivedpicture but the red signal which is required to keep the amplifier in balance would be'put into the scrap pile or part B.

I have chosen the particular embodiments described above as illustrative of my invention and it will be apparent that various other modifications may be made without departing from the spirit and scope of my in vention, which modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. .In televi sion transmission, the method which comprises scanning line by line the object whose image is to be transmitted,-pro- V ducing impulses during said scanning cordance with the shade variations 111 each line and producing at the end of each line an'auxiliary impulse whose magnitude substantially corrects any unbalance in light and dark portions of the line.

2. In television transmission, the method. -which comprises scanning line by line the object whose image is to be transmitted,-producing impulses during said scanning in accordance with the shade variations in .each line and producing an auxiliary impulse at the end of each line having-a value approximately proportional and opposite in sign to the average signal of that line.

which comprises scanning line by line the object whose image is to be transmitted, pro- 8t 3. In television transmission, the method ducing positive and negative impulses in accordance with the light and dark areas in each line and producing anauxiliary impulse at the end of each line in accordance with any inequality in the light and dark areas of said ne. 4. In television transmission, the method which comprises sc nning line by line the object whose image is to be transmitted, producing impulses during said scanning in accordance with the shade variations in each line, storingv energy during the -scanning of each line in accordance with the predominence of the light portions thereof and producing an auxiliary impulse at the end of each line substantially proportional to the stored energy.

5. Television transmission apparatus comprising means for scanning .the object whose image is to be transmitted, means for producing impulses in accordance with the shade variations in each scanning line, and means for producing an auxiliary impulse at the end of each line having a magnitude corresponding to the predominance of light or dark portions in said line.

6. Television transmission apparatus comprising means for scanning the object whose image is to be transmitted, means for producing impulses in accordance with the light and dark portions in each scanning line, and means for producing an auxiliary impulse at the end of each-line substantially proportional to any inequality in the impulses due to the light impulses and the dark impulses.

prising means forscanning the Object whose image is to be transmltte' 4 ducmg impulses in accordance with the h ht and dark portionsin e'ach'scanning line, and means for producing a corrective impulse at: the end. of each line comprising a condenser, 7

means for means for arying the charge thereof in accordance with the predominance of im ulsesfrom the light or the dark portions 0 said line and means for comparing the remaining charge of the condenser with a reference voltage source.

In witness whereof, I have hereto set my h hand this 16th day of September,' 1930.

ALDA- V. BEDFORD. 7 

